Monday, Allergan quoted several others voicing similar concerns, including some short sellers. But the show stoppers are the quotes Allergan cites from Morgan Stanley 's Robert Kindler, the bank’s global head of M&A, and David Horn, a health-care banker.

According to Allergan’s release, Mr. Kindler wrote in an email to Allergan executives:

“My takeaway is that AGN is not being nearly aggressive enough in going after the VRX business model and currency.”

And wrote Mr. Horn:

“Part of what Rob [Kindler] is suggesting [to Allergan] is to allow him to use his significant relationships with media and analysts to provide a clear and detailed articulation of why Valeant is a house of cards and your investors should not want to take their stock.”

The twist? Morgan Stanley hadn’t landed a role advising Allergan, and instead was hired this month by Valeant, as reported by CNBC last week.

Those emails are the kind bankers send when they are looking to get hired by a client. And it’s hardly surprising that Morgan Stanley would push to get on one of the biggest deals of the year. Allergan likely got dozens of such pitches from other investment bankers telling them to go after Valeant’s business model, an argument Allergan was even making to shareholders earlier this year when some speculation of a deal was percolating but before Valeant made its offer public.

Valeant, for its part, says its business model is more efficient and points to its dramatic stock growth. Tuesday morning, it will address shareholders with its fourth presentation since this fight started to “refute misleading assertions made by Allergan and others.”

Indeed, Morgan Stanley’s research arm actually has a buy rating on the stock.

Bankers regularly wind up pitching both sides in a deal, so there really isn’t much unusual about the exchange. There can be concerns about potential conflicts of interest in some instances. (Allergan is not raising such concerns about Morgan Stanley.)

For example: some large shareholders of diamond seller Zale Corp. recently tried to raise an issue when they saw in filings that company’s banker had pitched Zale’s eventual acquirer Signet Jewelers Ltd.

About Pharmalot

Pharmalot explores the fast-moving, complicated world that develops and markets medicines – and the drug makers that are attempting to replenish their pipelines while grappling with pricing and regulatory dictates, among many other challenges. Writer Ed Silverman has covered the pharmaceutical industry for nearly two decades and has closely followed the many hurdles facing drug companies as they move ideas from the laboratory to the medicine chest. He started Pharmalot while at The Star-Ledger of New Jersey and previously worked at New York Newsday and Investor’s Business Daily. Email Ed Silverman at ed.silverman@wsj.com, and follow him on Twitter @Pharmalot.